This invention relates to central hydraulic systems for marine deck machinery, and more particularly to a system providing both infinitely variable control of the operating speed of deck winches and fully automatic mooring winch operation.
It has long been recognized that the mooring lines used to connect a vessel to an adjacent pier or the like must be either paid out or taken in as the positioning of the vessel changes relative to the pier under the action of tides and similar factors. It is also considered necessary to accommodate selection of the line pull or tension of each mooring line on an individual basis. This is to facilitate mooring of the vessel in such a way that certain portions of the vessel are substantially prevented from moving with respect to the pier while permitting at least limited movement of other portions of the vessel. The necessity of providing selectable line pull is especially pronounced in the case of large vessels of the type known as super tankers because the extreme length of such vessels functions to multiply the effect of any motion of the vessel relative to the adjacent pier.
Systems for providing automatic mooring winch operation have been known heretofore. In one type of prior art system mooring winches are driven by electric motors equipped with electromechanical servo systems to provide automatic operation. Due to safety considerations this type of drive system cannot be utilized on vessels designed to transport liquified natural gas (LNG) and similar materials unless the electric motors are of the explosion-proof variety. The latter possibility is considered impractical due to the cost of explosion-proof motors.
Steam driven motors equipped with mechanical servo systems have also been utilized to provide automatic mooring winch operation. This is advantageous in one respect because steam generation is necessary on board tankers and similar vessels in order to effect cargo heating, cleaning of empty holds, etc. However, steam driven systems are now considered to be outmoded and for all practical purposes are no longer being specified for use on U.S. built vessels.
The prior art also includes hydraulic drive systems for marine deck equipment. Heretofore, these systems have utilized special reducing valves and relief valves in order to control the line pull or tension that is applied to the mooring line by the winch. This is considered unsatisfactory because any malfunction in the operation of these components, particularly with respect to the proper settings of the valves, can result in a complete burnout of the system. Also, certain prior art hydraulic drive systems have utilized dump valves to return excess pressurized hydraulic fluid to the storage reservoir and have therefore been highly inefficient.
The present invention comprises a novel drive system for marine deck equipment which fulfills the above-described operating requirements of such a system and simultaneously provides superior operating performance when compared with the performance characteristics of prior art systems. In accordance with the broader aspects of the invention, each marine deck winch is driven by a reversible hydraulic motor. The flow of pressurized hydraulic fluid to each hydraulic motor is regulated by an infinitely variable volume pressure compensated four-way directional valve to afford precise control over the speed of operation of the associated hydraulic motor and the marine deck winch driven thereby. The hydraulic motors which drive automatic mooring winches are variable displacement hydraulic motors. This permits individual regulation of the line pull or tension of the mooring line of each automatic mooring winch.
In accordance with more specific aspects of the invention, one or more variable displacement pressure compensated over center hydraulic pumps are used to supply pressurized hydraulic fluid for operating the hydraulic motors by means of a closed loop circuit. The infinitely variable volume pressure compensated four-way directional valve comprises pilot-operated valves, and hydraulic fluid at control pressure is supplied to the pilot ports at both ends of each valve. In certain embodiments of the invention hydraulic fluid from the variable displacement pressure compensated over center pumps is applied directly to the pilot ports of the valves, and pressure reducing apparatus is utilized to supply hydraulic fluid at working pressure. In other embodiments of the invention separate control pumps are utilized to supply hydraulic fluid at control pressure to the pilots ports of the infinitely variable volume pressure compensated four-way directional valves.
Each infinitely variable volume pressure compensated pilot operated four-way directional valve has associated therewith hydraulic circuitry for reducing the pressure in a selected pilot port of the valve and thereby actuating the valve to direct hydraulic fluid at working pressure to the associated hydraulic motor. This hydraulic circuitry includes at least one infinitely variable volume four-way directional valve for bleeding hydraulic fluid from a selected pilot port. The circuitry may include multiple valves connected in parallel and situated at spaced apart points on the deck of the vessel. Alternatively, mechanical linkages may be provided for operating a single valve from spaced apart points on the deck of the vessel.
Each marine deck winch of the vessel is provided with a brake which functions to prevent operation of the winch whenever the associated hydraulic motor is not operating. Each brake is provided with a hydraulic actuator which functions to disable the brake whenever the associated infinitely variable volume pressure compensated pilot operated four-way directional valve is actuated to direct pressurized hydraulic fluid to the hydraulic motor. In certain embodiments of the invention the pressurized hydraulic fluid which is directed to the hydraulic motor is also directed to the hydraulic actuator of the associated brake through a sequence valve. In other embodiments of the invention pressurized hydraulic fluid is continuously directed to the hydraulic actuator of each brake and a valve adapted for operation in concurrence with the operation of the associated infinitely variable volume pressure compensated pilot operated four-way directional valve to pressurize the associated hydraulic motor is utilized to control operation of the hydraulic actuator. The valve which controls the operation of the hydraulic actuator may comprise either a valve mechanically linked to the infinitely variable volume pressure conpensated pilot operated four-way directional valve or a pilot operated valve coupled in parallel with the infinitely variable volume pressure compensated pilot operated four-way directional valve for operation in synchronism therewith.
The drive system further includes one or more charging pumps for supplying hydraulic fluid at charging pressure. In certain embodiments of the invention the infinitely variable volume pressure compensated pilot operated four-way directional valves comprise open center valves, in which case hydraulic fluid at charging pressure is supplied through the open center of the valve to the associated hydraulic motor whenever the hydraulic motor is not operating. In other embodiments the infinitely variable volume pressure compensated pilot operated four-way directional valves comprise closed center valves, in which case hydraulic circuitry is provided for directing hydraulic fluid at charging pressure to the hydraulic motors when they are not operating. In both embodiments hydraulic fluid is continuously drained from the motors and from the hydraulic circuitry which is utilized to operate the infinitely variable volume pressure compensated pilot operated four-way directional valves. By this means any possibility that the system will be disabled due to clogging by low temperature hydraulic fluid is completely eliminated.